Grainger Family Research

Looking for any history of the Grainger family from Tasmania. I recently started my family tree and in doing so found and met my father, Kevin Lloyd Grainger, also his brother Horace William "Bill" Grainger.(Both now deceased) Their father is the problem. I think he was born William Douglas 12/04/1900 in Lefroy, Tas to William Grainger and Catherine "Kate" nee West. William, his father, passed away 28/04/1917 from there he joined the army (underaged), with his brother Roy Charles signing as his guardian,and calling himself Thomas Henry Grainger, service no. 2401, with the same NOK, sister Violet, as another brother Horace(Australian Imperial Force - Nominal Roll). Then it just gets better!After the war he reverted back to William Henry, not William Douglas, marriage certificate confirms. He died in a Sydney mental/military hospital as Thomas Henry, 2401, around 1935. Any information from here would be appreciated.